Method for separating impurities out of feed stock in copper melts

ABSTRACT

The invention relates to a method for separating impurities out of slags, dusts, minerals, preparation residues of minerals or of recyclings or remaining substances, subsequently called feed stock. In order to save energy and reduce costs, the inventive method is characterized by the combination of the following features: melting the feed stock containing the impurities; forming a copper melt; bring the feed stock into contact with the copper melt while adding reducing agents, preferably coke and/or coal; vaporizing, if required, existing volatile compounds such as metal chlorides; reducing metals of the feed stock more noble than copper in the copper melt, and; forming a slag with constituents of the feed stock to be purified that is less noble than copper.

The present application claims the benefit of the filing date of Austrian Patent Application A1433/2005—filed Sep. 1, 2005, the disclosure of which is hereby incorporated herein by reference.

This invention relates to a method for separating impurities out of slag, dust, minerals, preparation residues of minerals or out of recyclings or remaining substances. All these substances to be purified are subsequently called feed stock.

Fusion metallurgy treatment methods in which iron melts are used to take up impurities are known for the purpose of separating impurities. A method of this type is described, for example, in AT 412 283 B. The aim of the method is to form environmentally compatible slag from iron-containing blast-furnace residue and to recover the iron fraction contained therein. For this purpose the residue is reduced in or over an iron melt by the carbon dissolved in the iron melt. Iron oxide and other metal oxides are reduced and recovered from the iron metal. After dephosphorization, the resulting metal can be used as a replacement for pig iron produced in a blast furnace or if the Cr/Ni contents are high, it can be used as a working resource for stainless steel production. The slag produced can be used as a clinker replacement in the cement industry.

According to WO 97/29214 A, residue or slag from rubbish incineration or pyrolysis is heated together with chlorine or chlorine-containing substances under reducing conditions to temperatures above 650° C. whereupon volatile metal chlorides such as heavy metal chlorides (PbCl₂, ZnCl₂, CuCl₂) are removed in the gas phase. The remaining solid residue is mixed with steel slag or lime marl. The mixed slag is reduced over a turbulent iron bath. In this case a synthetic blast furnace slag with hydraulic properties and a carbon-saturated iron alloy can be produced. The iron alloy obtained forms a feed stock for the steel industry. Alternatively a carbon-free, highly enriched ferro-chromium alloy can be obtained by fractional reduction.

JP 11207288 likewise describes a smelting method for the treatment of residue from rubbish incineration. In this case, the incineration residue is charged in an electric arc furnace into a metal bath which substantially consists of iron. A slag layer is thereby formed. Slag and metal are jointly extracted continuously and supplied to a water bath. Separation takes place by means of a magnetic separator. The metal contains a relatively large amount of copper and can be used as copper raw material.

In said methods which specify utilisation in the steel industry for contaminated iron melts, the enrichment by metals nobler than iron, for example, copper or tin is disadvantageous. These metals can no longer be removed economically and above certain limiting contents, present problems for further use of the iron melt. According to AT 412 283 B, for example, a high-quality pig iron bath system is used and this is contaminated with nobler metals after treatment of the residue. This deterioration in quality can have the result that use in the steel industry is no longer possible.

When using a pig iron bath system, an oxidising procedure has a disadvantageous effect. The carbon dissolved in the pig iron would thereby escape in the form of CO/CO₂ and thus the melting temperature would increase above 1500°. In order to prevent solidification of the melt when adding the residue, the required processing temperature must be significantly higher. At such high temperatures, the stressing of the refractory furnace lining and the increased energy requirement has a disadvantageous effect.

The purpose of the invention is to avoid these disadvantages and its object is to provide a method for separating impurities from slag, dust, minerals, preparation residues of minerals or from recyclings or remaining substances, subsequently called feed stock, in which deterioration in quality is avoided in a process extending over a fairly long time or in a plurality of successive process cycles. In addition, the method should allow energy savings compared with known methods and furthermore allow costs savings in that refractory linings of reactor vessels in which the process is carried out have a long life.

This object is achieved by the following combination of features:

-   -   melting the feed stock containing the impurities;     -   forming a copper melt,     -   bringing the feed stock in contact with the copper melt while         adding reducing agents, preferably coke or coal,     -   vaporising if required existing volatile compounds such as metal         chlorides,     -   reducing metals of the feed stock more noble than copper in the         copper melt and     -   forming a slag with constituents of the feed stock to be         purified that is less noble than copper.

The copper melt preferably has a minimum content of 50% copper.

The use of a copper melt has the advantage that the impurities which cannot be removed from an iron melt can easily be removed from a copper melt in a normal copper recycling process. In this way, the contaminated copper melt can be processed to high-quality copper again. A particular advantage of using a copper melt is its low melting point compared to an iron melt. As a result, the processing temperature of the feed stock is primarily determined by the melting point of the slag. It is thereby possible to maintain low processing temperatures when carrying out the method, which is reflected in lower energy costs and in conservation of refractory linings of the metallurgical vessel in which the method is carried out.

The copper melt can optionally be purified by blowing oxygen directly into the metallurgical vessel in which the method is carried out. In this case, the impurities less noble than copper form a slag. As a result of its high copper content, the slag thus formed can be used for separating impurities from feed stock at the beginning of a following process.

It is particularly advantageous for the method according to the invention to use scrap copper for producing the copper melt since scrap copper is fed to the copper recycling process anyway.

The copper melt can be formed by melting copper-containing waste material. For this purpose new scrap (fabrication waste) and/or old scrap of copper and/or copper alloys can be formed. Part of the copper melt can be formed by adding slag produced by blowing oxygen into the copper melt, as has been mentioned above.

The slag formed from the feed stock to be purified is preferably processed using adjuvants and/or waste materials to form clinker substitute and/or sand blasting abrasives.

Dust from waste incineration and from the iron and steel industry can be used as feed stock to be purified.

Anodic sludge accumulating during electrolytic refining in the course of copper recycling is advantageously used as feed stock to be purified.

As has already been mentioned, preferably coke and/or coal are used as reducing agents for the feed stock but substances less noble that copper such as metallic waste materials e.g. aluminium-containing waste materials and/or iron-containing waste material can be used as reducing agents.

When using a copper melt, it is advantageously possible to adjust various atmospheres above said melt; both reducing and oxidising conditions can be adjusted. The atmosphere can also be varied over the duration of the process, whereby undesirable contents of the impurities can be specifically separated.

The feed stock to be purified together with the reducing agents are preferably injected into the copper melt.

The formation of a copper melt and the melting of the feed stock and the addition of the reducing agents can take place simultaneously or successively. For example, it is also possible that the feed stock to be purified is applied to a hot copper block which has not yet melted, preferably in layers, and any metal chlorides that may be present are thereby vaporised, whereby a halogenating atmosphere is preferably adjusted, preferably using a chlorine-containing flushing gas.

The copper block together with the feed stock to be purified is then melted and reducing agents are introduced into the melt, preferably are injected via lances.

The method according to the invention is explained in detail with reference to the description of two variants. The two variants show ways which are feasible in principle for using a copper melt.

Variant 1

The feed stock to be treated is injected into a copper melt located in a metallurgical vessel together with a reducing agent. Coal or coke, for example, can be used as reducing agents.

TABLE 1 Reducing agents Coke Coal Component [%] [%] C 91.15 87.10 SiO₂ 2.88 2.20 Al₂O₃ 1.91 1.25 CaO 0.36 0.39 MgO 0.12 0.09

Metals in the feed stocks which are less noble than copper are also used as reducing agents. In addition, metallic reducing agents in the form of metallic waste materials, for example, aluminium or iron filings can be added, where the fraction of aluminium or iron is preferably at least 80%.

The copper melt is produced by melting copper-containing waste material. Predominantly considered for this purpose is new waste (fabrication waste) or old waste of copper and copper alloys (for example, brass, bronzes, red brass, nickel silver) including chippings and dust. The preferred copper content in the feed stock is at least 50%. Table 2 gives the composition of a brass and a bronze waste as examples.

TABLE 2 Copper-containing waste material Brass waste Bronze waste Element [%] [%] Cu 60.19 94.49 Zn 37.62 Pb 0.63 Sn 0.42 4.77 Fe 0.2 Al 0.21 0.039 Ni 0.13 Si 0.023 0.016 Sb 0.006 Mn 0.038 0.0023 P 0.007 0.18 As 0.015 S 0.21 Pb 0.008

The method according to the invention can be used to process contaminated dust, slag and minerals of different origin, in particular dust from rubbish incineration and slag or dust from the iron and steel industry. Lead or coloured glass waste, scrap catalysts and processing residue of minerals such as, for example, roasting residues (e.g. pyrite combustion) can also be used. Material cleared from furnaces which has been infiltrated with noble metals (e.g. Pt, Au, Ag) can also be processed with the method according to the invention.

In the course of copper recycling, the noble metals (Pt, Ag, Au) are deposited in the anodic sludge during electrolytic refining. The noble metals can be recovered from the anodic sludge by means of the method according to the invention and reused. Noble-metal-containing feed stock such as, for example, the aforementioned material cleared from furnaces thus make a decision contribution to improving the economic efficiency of a copper refinery.

Example compositions are given in the following tables:

TABLE 3 Dust from rubbish incineration Fly ash from Fly ash from incineration rubbish incineration of special rubbish Element [mg/kg] [mg/kg] Ca 107000 47985 Cl 74000 33370 Si 160000 54804 Mg 15000 8041 Fe 25000 43763 Al 71000 17302 K 36000 47485 Na 31000 154364 Zn 28000 68165 S 26000 81929 Pb 11000 19527 Ti 8700 18332 Mn 1300 1992 Ba 1700 124 Sn 1400 2741 Cu 1200 6340

TABLE 4 Slag and dust from the iron and steel industry LD EAF Blast furnace Converter Slag dust dust dust Component [%] [%] [%] [%] CaO 50  5-12 6.3 3-5 SiO2 15 6.3 Al2O3 <2 2 MgO <3 Fe 16 20-30 34.4 50-70 MnO <4 P2O5 <2 Cr_(tot) <1 0.1-0.4 C 28.9 20-50 Pb 1-8 0.07 0.2-0.5 Zn 15-35 0.2 1-3

TABLE 5 Residue from other branches of industry Catalytic Pyrite converter combustion Lead glass (car indus- (sulphuric acid waste (glass try) production) [%] industry) [%] [%] Fe 55 SiO₂ 56 Pt 0.14 Zn 2.8 PbO* 32 Pd 0.07 Cu 1.3 K₂O 11.4 Rh 0.015 S 2.6 Al₂O₃ 0.1 Carrier Residue material Pb 0.5 As₂O₅ 0.5 Waste 10.00 rock Co 0.12 Ag 0.004 Au 0.0001 Cd 0.005 Tl 0.003 P 0.11 *The PbO content can be 3-32% depending on the type of glass

The components of the feed stock are divided by the treatment process into copper bath, slag or waste gas according to their composition.

Metals in the feed stock which are nobler than copper are reduced and remain in the copper melt. Less noble components are transferred into the slag located above the melt. Volatile compounds in the feed stock such as, for example, metal chlorides, in particular zinc chloride and lead chloride, vaporise.

At the end of the treatment process the slag is adjusted with adjuvants or waste materials so that it can be used as clinker substitute or as sand blasting abrasive. The slag is then tapped and charged into a dry granulator. The granulation can take place by separating the slag stream on a rotary plate into fine droplets, which then solidify in a glass-like manner in the air stream. The copper melt is also tapped and fed to the copper recycling process whereby copper and the noble metals contained therein can be recovered from the melt.

The copper bath can optionally be purified by blowing oxygen directly into the melt system. The impurities which are less noble than copper thereby form slag. As a result of the high copper content, the slag thereby formed can be fed together with the scrap copper at the beginning of the process.

Variant 2

A block of scrap copper is heated in the melting system. Advantageously solidified residual copper melt from the previous treatment can be used for this. As in variant 1, the copper melt is produced by melting copper-containing waste material. The feed stock to be treated is applied in layers to the copper block. When using residual copper melt, charging can begin immediately after the surface of the copper bath has solidified. The heat of the cooling copper bath can be used to vaporise metal chlorides present in the feed stock. A halogenating atmosphere can be used for assistance, for example, using a chlorine-containing flushing gas. The flushing gas is blown onto the residue from above. Alternatively the residue can be roasted with chlorine or chlorine-containing substances under reducing conditions.

In this case, metal chlorides can be vaporised from the feed stock. The gas phase can be purified in the usual manner whereby the metal chlorides are retained in filters. The heavy metals can be recovered in a known manner (electrolysis, extraction).

The remaining metal compounds in the feed stocks can be removed by subsequent purification under reducing conditions. For this purpose the feed stock and the solidified copper melts are melted. Reducing agent is fed into the copper bath by means of lances (see Variant 1).

The copper melt and the slag can undergo further treatment as in variant 1. 

1. A method for separating impurities from slag, dust, minerals, preparation residues of minerals or of recyclings or remaining substances, subsequently called feed stock, the method comprising the following features: melting the feed stock containing the impurities; forming a copper melt, bringing the feed stock in contact with the copper melt whilst adding reducing agents, preferably coke or coal, vaporising if required existing volatile compounds such as metal chlorides, reducing metals of the feed stock more noble than copper in the copper melt and forming a slag with constituents of the feed stock to be purified that are less noble than copper.
 2. The method according to claim 1, wherein a copper melt is formed with at least 50% copper.
 3. The method according to claim 1, wherein after reduction and taking up metals more noble than copper originating from the feed stock, the copper melt is subjected to a copper recycling process.
 4. The method according to claim 3, wherein the copper melt is recycled by blowing in oxygen.
 5. The method according to claim 1, wherein the copper melt is formed by melting scrap copper and/or by melting old or new scrap of copper and/or copper alloys and/or a part of the copper melt is formed by adding slag produced by blowing in oxygen into the copper melt.
 6. The method according to claim 1, wherein the slag formed from the feed stock to be purified is processed using adjuvants and/or waste materials to form clinker substitute and/or sand blasting abrasives.
 7. The method according to any one of claims 1 to 6, characterised in that dust from waste incineration is used as feed stock to be purified.
 8. The method according to claim 1, wherein dust from the iron and steel industry is used as feed stock to be purified.
 9. The method according to claim 1, wherein anodic sludge accumulating during electrolytic refining in the course of copper recycling is used as feed stock to be purified.
 10. The method according to claim 1, wherein substances less noble than copper are used as reducing agents.
 11. The method according to claim 1, wherein metallic waste materials such as aluminium-containing waste materials and/or iron-containing waste material are used as reducing agents.
 12. The method according to claim 1, wherein a reducing or oxidising atmosphere is adjusted above the copper melt.
 13. The method according to claim 1, wherein the feed stock to be purified together with the reducing agents are injected into the copper melt.
 14. The method according to claim 1, wherein the feed stock to be purified is applied to a hot copper block which has not yet melted and any metal chlorides that may be present are thereby vaporised.
 15. The method according to claim 14, wherein a halogenating atmosphere is adjusted, preferably using a chlorine-containing flushing gas.
 16. The method according to claim 14, wherein the copper block together with the feed stock to be purified is melted and reducing agents are introduced into the melt, preferably are injected via lances. 